The objectives of the proposed collaborative, multidisciplinary studies are: 1) to elucidate the effects of dietary fats, cholesterol, proteins, and complex carbohydrates on composition, physical properties, and morphology of high density lipoproteins (HDL) and their distribution and concentration in plasma; 2) to relate these dietary effects on HDL to changes in properties and distribution of other lipoprotein classes, to activities of lipolytic enzymes, and to levels of plasma hormones that may modify or determine individual differences in response to diet; 3) to determine the effects of an acute fat meal and of changes in total energy flux on HDL and other lipoproteins and to relate these effects to diet composition, lipolytic activities, and plasma hormone levels. Diets consisting of purees of real foods will be fed to free-living and confined normolipemic, non-obese, healthy men for four-week periods. Each out-patient study group (n equals 6) will be fed a basal diet (fat 30%, P/S ratio 1, cholesterol 400 mg, carbohydrate 55%, protein 15%), and two other diets in which fat content, P.S ratio, cholesterol content or protein source (animal vs vegetable) will be varied isocalorically. All subjects will be fed a standard fat meal at the end of each diet period. In confined studies, changes in total energy flux will be achieved by varying energy intake and activity level at constant weight. HDL, HDL subspecies and other lipoproteins will be measured by analytic ultracentrifugation and other standard methodologies. Lipid and apoprotein composition and morphology of isolated lipoproteins will be analyzed in detail. Lipase activities and effects of in vivo lipolysis will be measured after intravenous heparin. The results will provide thorough characterization of diet-induced changes in HDL and other lipoproteins which will allow better design and interpretation of diet therapies aimed at reducing risk of cardiovascular disease.